Penny is heading upstairs with laundry and meets a woman staring at the broken elevator pondering the implications. "You must be Leonard's mother,” remarks Penny. She replies "Well, I don't know if I must be, but yes."

The woman introduces herself as Dr. Beverly Hofstadter. As they climb the stairs together, Penny starts to ask about Leonard as a child and learns about his penis grasping at age five. After Beverly learns that she is an actress she observes that, “There are many studies that suggest that people who go into the performing arts suffer from an external locus of identity." By the time they reach Leonard’s apartment, she is in tears talking about her own childhood and trying to win her father’s approval.

Leonard is not surprised by Penny’s reaction as he invites his mother in. He makes tea for her to exact instructions just like Sheldon does, however it was now cold. Beverly only had sex with her husband for procreation which they wrote papers about. Sheldon wants to hear more about her sex life. He can get the papers from the Princeton University Press; however the PowerPoint slides are on her other laptop. Sheldon and Leonard debate about their mothers. Sheldon finds Beverly fascinating and Leonard had the childhood that he wanted.

Lunch with Beverly.

At Caltech, Beverly is having lunch with the gang. After Howard asked, Beverly replied that, Leonard’s two siblings are far more successful than he is. Dr. Hofstadter confirms that his younger brother, Michael, is a law professor teaching at Harvard and his sister successfully grew a pancreas in an adolescent gibbon. “You must be very proud," replied Howard. "Why? They're not my accomplishments.“ Beverly leaves with Leonard telling them how hard they are making things on him. Upon her return Leonard tells her about Raj’s inability to talk to women and Howard living with his mother. "That's fascinating. Selective mutism is quite rare. On the other hand, a Jewish male living with his mother is so common, it borders on sociological cliche. You know, both selective mutism and an inability to separate from one's mother could be due to a pathological fear of women. That's would explain why the two of you have created an ersatz homosexual marriage to satisfy your need for intimacy." At one o’clock she insists that Leonard show her his lab as he had promised even though he wants her to torture his friends. Describing his work as trying to reproduce the dark matter research performed by an Italian team, she tells him that she doesn't need to see his work, just get her a copy of their paper.

Leonard now could really use a drink, so he goes over to Penny’s who is well ahead of him due to her analysis by Beverly. Beverly and Sheldon went to the hospital so that she could scan Sheldon’s remarkable brain. Penny had also had not gotten an anti-depressant commercial because she was too perky. Leonard describes more of his miserable childhood and how he built a hugging machine which had two radio controlled airs just to have some human contact. Worst yet, his father used to borrow it.

Penny and Leonard driven together by Leonard's mother

Sheldon and Dr. Hofstadter return from the hospital and relax in his apartment. Sheldon seems to have developed quite the rapport with Dr. Hofstadter and is quite comfortable around her as is Beverly.

Penny and Leonard are feeling no pain downing tequila shots and are in a very good mood. She has him lick the salt off her neck, take a shot and bite the lime. He lingers on her neck, takes the shot and finds the lime in Penny’s mouth. He goes after the lime and they start making out passionately.

Back in Apartment 4A, Beverly is contemplating Sheldon's "suggestion." She is not sure if it's appropriate with her son's roommate, but they both agree they'd be very good together.

Sheldon and Beverly rocking out together.

Penny and Leonard have worked their way into bed. Leonard says that he can’t believe it going to happen. She tell him to shush and he goes with "You know what my mother would say about this. She'd say because since you were not loved by your father and I was not loved by my mother that having sex is our way of making up for the intimacy we didn't get as children." This revelation stops Penny cold telling him that that is the sickest thing she has ever heard. She realizes what she is doing, and horrified at the thought of using Leonard to take her mind off her childhood problems, tells him to leave. Leonard is next seen getting thrown out of her apartment. After feeling terrible that he didn't keep his big mouth shout, he finds his mother and Sheldon using Rock Band doing "Any Way You Want It” with gusto.

However in the morning, Penny wants to give Leonard an explanation and an apology for her actions, but Leonard understands what she is talking about and begs her never to talk of the night before ever again. Penny runs into Beverly when she is leaving and again is in tears by the time they reach the lobby. She wants Penny to have sessions with her, provided Penny is willing to go to New Jersey and go through a brain scan while doing so.

"Yet another consistent episode of comedy. You can’t help but laugh at the carefully crafted dialogue and attention to detail. But I can’t help but wonder what this show would be capable of with more characterization."[1] The TV Critic's Review

In the final scene, Beverly and Penny walk downstairs as Penny is leaving for work, and Beverly is going to the airport to go home. As they approach the first floor landing area, Penny says to Beverly (she's crying again and giving Beverly more information about her childhood and her issues), "My mom could have just said, 'Bob, get over it; she's a girl, move on'". This reveals that "Bob" is her Dad, but in "The Boyfriend Complexity", we are introduced to her father and his name is Wyatt.

[The gang, except for Leonard, are in the apartment's living room. Leonard enters the room, talking on his cell phone, and the gang overhear his side of the conversation.]

Leonard: I’m really very busy. Is there any way that we can put this off until I have more time to prepare? Of course. But, uh, you understand my trepidation.

Penny: What’s that about?

Howard: Not a clue.

Leonard: Can’t we just postpone it till the spring? Maybe next summer?

Sheldon: This should be fairly easy to deduce. He’s holding the phone to his left ear. Ears do not cross hemispheres, so he’s using the analytic rather than the emotional side of the brain, suggesting that he has no personal relationship with the caller.

Leonard: No, I didn't realize it had been so long. Sure, I guess there’s no other choice, but to just go ahead and do it.

Sheldon: He’s referring to an activity he has done before. It’s unpleasant and needs to be repeated. This suggests some sort of invasive medical test, like perhaps a colonoscopy.

Leonard: Aren't there any other options? There’s not a lot of room, it’s gonna be uncomfortable.

Sheldon: Yes, yes. I’m definitely going with colonoscopy.

Leonard: Okay, bye. [ends the call and turns to speak to the rest of the gang] My mother’s coming to visit.

Howard:[to Sheldon] How about that, you were right.

[After starting her laundry, Penny walks upstairs from the basement to the lobby. She notices a tall, bony woman with glasses, medium-length hair and a suitcase, staring at the elevator.]

Penny: It's out of order.

Woman: Yes, I can read the sign. I'm just pondering the implications.

Penny: I think it implies that the elevator doesn't work.

Woman: Again, I can read the sign. But the sign and the tape are covered with a layer of dust which indicates that the elevator has been non-functional for a significant amount of time which suggests either a remarkable passivity among the, I assume, 24 to 36 residents of this building based on the number of mailboxes and given typical urban population density, or a shared delusion of functionality.

[Penny stares at her a short while, until she realizes who she must be.]

Penny: You must be Leonard's mother.

Woman: Oh, I don't know if I must be, but yes.

Penny: Um, I'm Penny. I'm his neighbor.

Woman: Oh. Dr. Beverly Hofstadter.

Penny: Oh, nice to meet you. [Puts her hand out for Beverly to shake.]

Beverly: Oh, you're a hand shaker. Interesting.

Penny: Um, why don't you come with me. I'll walk you to the apartment.

Beverly: Oh, all right. Would you like to exchange pleasantries on the way?

Penny: Yeah, sure, I guess.

Beverly: All right, you start.

[They both walk up the stairs together.]

Penny: Okay. You know, I've always been curious. What was Leonard like when he was little?

Beverly: Oh, I think you mean young. He's always been little.

Penny: Right, Okay, what was he like he was young?

Beverly: You'll have to be more specific.

Penny: Oh, um... Okay, like, five or six.

[Beverly stares at her coldly.]

Penny: Five.

Beverly: Oh. Well, at that age, he was well enmeshed in what Freud would call the phallic stage of psychosexual development. An outmoded theory, of course, but the boy did spend most his waking hours with a tight grasp on his penis.

Penny: Oh yeah, Leonard mentioned you were a psychiatrist.

Beverly: Well, that is one of my degrees. My primary field is neuroscience.

Penny: Oh. Well, I'm an actress.

[There is a short silence between the two.]

Beverly: Why?

Penny: What do you mean, why?

Beverly: There are studies that suggest that many who go into the performing arts suffer from an external locus of identity.

Penny: Yeah, I don't know what that means.

Beverly: Well, it means you value yourself only as others value you, which is often the result of unmet childhood emotional needs.

Penny: Oh. Well, I had a wonderful childhood.

Beverly: Tell me about it.

[By the time they get to Leonard's and Sheldon's apartment, Penny is in absolute tears, talking about her dad.]

Penny:[sobbing] I know my dad wanted a boy! I, I just, I tried being good at sports, but I hated getting dirty!

Beverly: And then I'm assuming you entered adolescence.

Penny: Uh-huh, he called me Slugger until I got my first training bra and then he just stopped playing catch with me! I wasn't Slugger anymore!

[Penny knocks on the apartment door and Leonard answers.]

Penny:[to Leonard, as she gives vent to a huge sob] Your mother's here!

[Penny, still crying, goes to her apartment.]

Beverly:[to Leonard] If you want to have intercourse with that girl, find out what kind of cologne her father wore.

Leonard: Good to see you, Mother.

[Leonard's mother Beverly has just arrived at the apartment.]

Leonard: Here's your tea, Mother.

Beverly: Oolong?

Leonard: Yes.

Beverly: Loose, not bagged?

Leonard: Yes.

Beverly: Steeped 3 minutes?

Leonard: Yes.

Beverly: 2% milk?

Leonard: Yes.

Beverly: Warmed separately?

Leonard: Yes.

Beverly: One teaspoon of sugar?

Leonard: Yes.

Beverly: Raw sugar?

Leonard: Yes.

[Beverly takes a sip.]

Beverly: It's cold.

Leonard: I'll start again. [He goes to the kitchen.]

Sheldon: I have the same problem with him. My theory is that his lack of focus stems from an overdeveloped sex drive.

Beverly: Oh, I don’t know where he would've gotten that. Aside from a pro forma consummation of our marriage, his father and I only had intercourse for the purposes of reproduction.

Sheldon: That seems a fairly efficient arrangement.

Beverly: Yes, we think so. We've both done papers on it. Mine from the neuroscientific point of view and his from an anthropological. Mine, of course, was the only one worth reading.

Sheldon: Of course. I would very much like to read about your sex life.

Beverly: Well, it’s all online, or you can order it from the Princeton University Press.

Beverly: That’s fascinating. Selective mutism is quite rare. On the other hand, an adult Jewish male living with his mother is so common it borders on sociological cliche.

Howard: It’s just temporary. I pay rent.

Leonard: He lives in the same room where his bassinet was.

Beverley: You know, both selective mutism and an inability to separate from one’s mother can stem from a pathological fear of women. It might explain why the two of you have created an ersatz homosexual marriage to satisfy your need for intimacy.

Howard: Say what? [Raj whispers in his ear] That’s basically what I just said!

Sheldon: What are the odds that two individuals as unique as ourselves would be connected by someone as comparatively workaday as your son?

Beverly: Is that a rhetorical point or would you like to do the math?

Sheldon: I’d like to do the math.

Beverly: I’d like that, too.

[In Penny's apartment, Leonard and Penny have switched from wine to tequila shots.]

Penny: You’re gonna lick the salt off my neck, do the shot, and then bite the lime. [She sprinkles salt on her neck.]

Leonard:[drunkenly] I’m sorry, I didn't hear anything after lick.

Penny:[pointing to each item in sequence] Neck, shot, lime.

[Leonard licks the salt off of Penny's neck, taking his time about it. After several seconds, Penny decides it's been long enough.]

Penny: Okay. Shot, lime.

Leonard: Right. [does the shot] Ah! Where’s the lime?

[Penny grins, revealing that she has the lime clenched in her teeth.]

Leonard: Oh. Okay, we’re sharing.

[Leonard leans close to Penny to bite the lime. Inevitably, they end up kissing. After a few seconds, Leonard breaks off the kiss, turns away from Penny, spits out the lime, and then returns to kissing her.]

[Meanwhile, in Sheldon's and Leonard's apartment, Beverly and Sheldon are deep in thought.]

Sheldon: Normally, I’d feel the same way. But based on everything I've observed about us, I can’t help but speculate we’d be very good together.

Beverly: True. I've had a similar observation. It’s certainly something I could never do with my husband.

Sheldon: I was hesitant the first time I tried it, but I experienced an unanticipated and remarkable release of endorphins. It’s quite satisfying.

Beverly:[smiling] I see what you’re doing. You’re appealing to the neuroscientific researcher in me.

Sheldon: You see right through me, don’t you?

Beverly: Only when you’re in a CAT scanner.

[Back in Penny's apartment, Leonard and Penny are in Penny's bed. Their rendezvous has obviously gotten more heated, as Penny has removed her shirt and is now in her bra.]

Leonard: This is actually gonna happen.

Penny: Honey, shush. Shush, shush, shush, shush.

Leonard: You shush. I’m happy. I don't want to talk about it. You know what my mother would say about this? She would say because you were not loved by your father and I was not loved by my mother, that having sex is our way of making up for the intimacy we didn't get as children.

Penny:[annoyed]Why would you bring that up right now?

Leonard: I don’t know. Foreplay?

Penny: So you’re saying you’re not having sex with me, you’re having sex with your mother?

Leonard: Ummm, I’m gonna go with "no".

Penny: That is the sickest thing I've ever heard.

Leonard: Come on. You’re trying to have sex with your father, and I’m okay with that.

[The scene abruptly shifts to Penny's front door. Leonard is being bodily pushed out the door and into the hallway.]

Penny:[from inside her apartment] GET OUT!

Leonard: She said shush. I should have shushed.

[He goes back into his own apartment, where loud music is playing. He is then befuddled at the sight of Sheldon and Beverly completely absorbed in a jam session, using a karaoke machine to perform a duet of Journey's "Any Way You Want It".]

[The next morning, Beverly is leaving. She and Leonard are saying their goodbyes in the hallway.]